oh so I suppose a similar approach as the european folk song? ie. you have a chorus that repeats and maybe a few verses that are widely known to start with but you can improvise the lyrics afterwards to stretch out the performance until you're out of ideas, while melody of each verse stays the same ish.
perhaps with a more loose framework?
i guess they are folk songs in a way, a lot of the sounds and i guess the lyrics have deep roots. Some artists have done studio recordings, but they are seen as not properly professional music as they are mainly heard performed at weddings, funerals, and quite a different style to arabic pop, though there's not a very clear boundary.
some musicians get famous with this style like shaaban and adawia, but the establishment (the Egyptian musician's union among others) rejects them and polite society sneers at them, the music is said to be "sha'abi", meaning popular as in "people's" with the connotation of "street" and low class. (I think they have "shaabi" music in Algeria and Morocco too, same word, but not quite the same derisive meaning, and a different musical style, i believe)
the most recent iteration of that conflict (which all plays out in the mainstream of Egyptian culture, so is at least some extent a fake dispute stoked up by everyone involved for their own ends) is the mahragan artists i posted in COTD a couple of months ago. So what i had in mind was more like rappers or grimers than folkies, tbh - that incessant shouting!
That rejection frees up sha'abi artists to be rude and sleazy, so there's a split there between the likes of megastars like Amr Diab or Nancy Ajram. who are held to high standards of public conduct, whereas this lot get to sing about hash and booze and girls, as well as to appear on TV as sort of naughty characters. There's a lot of contradiction and hypocrisy which is right in your face when you see a wedding singer on stage accompanied by a bunch of listless belly dancing women, while the audience is 90% slavering young guys and possibly a small segregated group of conservatively clad women.
I'm not good enough at music or arabic to comment in more detail or more authoritatively about the form or the melodies etc, but the stripped down echoey sound, the late night back street aesthetic and the rawness and wild virtuosity speaks for itself i think